1. Field of the Invention
The present invention relates to an aromatic block polycarbonate resin which is useful as the photoconductive material for use in the electrophotographic photoconductor, and the production process of the aromatic block polycarbonate resin. The present invention also relates to a diphenol compound used to produce the above-mentioned polycarbonate resin, and the production process of the diphenol compound. Further, the present invention relates to an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer formed thereon, comprising the above-mentioned aromatic block polycarbonate resin. In addition, the present invention also relates to an electrophotographic image forming apparatus and method using the above-mentioned photoconductor, and a process cartridge which is freely attachable to the image forming apparatus and detachable therefrom.
2. Discussion of Background
Conventionally known representative aromatic polycarbonate resins are obtained by allowing 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) to react with phosgene or diphenylcarbonate. Such polycarbonate resins made from bisphenol A are used in many fields because of their excellent characteristics, such as high transparency, high heat resistance, high dimensional accuracy, and high mechanical strength.
For example, this kind of polycarbonate resin is intensively studied as a binder resin for use in an organic photoconductor in the electrophotographic field, Recently organic photoconductors (OPC) are used in many copying machines and printers. These organic photoconductors have a layered structure comprising a charge generation layer (CGL) and a charge transport layer (CTL) which are successively overlaid on an electroconductive support. The charge transport layer (CTL) comprises a binder resin and a low-molecular-weight charge transport material (CTM). The addition of such a low-molecular-weight charge transport material (CTM) to the binder resin lowers the intrinsic mechanical strength of the binder resin, so that the CTL film becomes fragile. The result is that the abrasion resistance of the photoconductor is lowered, so that scratches and cracks are easily formed on the surface of the photoconductor. The durability of the photoconductor is thus impaired.
Although some vinyl polymers such as polyvinyl anthracene, polyvinyl pyrene and poly-N-vinylcarbazole have been studied as high-molecular weight photoconductive materials for forming a charge transport complex for use in the conventional organic photoconductor, such polymers are not satisfactory from the viewpoint of photosensitivity.
In addition, high-molecular weight materials having charge transporting properties have been also studied to eliminate the shortcomings of the above-mentioned layered photoconductor. For instance, there are proposed an acrylic resin having a triphenylamine structure as reported by M. Stolka et al., in “J. Polym. Sci., vol 21, 969 (1983)”; a vinyl polymer having a hydrazone structure as described in “Japan Hard Copy '89 p. 67”; and polycarbonate resins having a triarylamine structure as disclosed in U.S. Pat. Nos. 4,801,517, 4,806,443, 4,806,444, 4,937,165, 4,959,288, 5,030,532, 5,034,296, and 5,080,989, and Japanese Laid-Open Patent Applications Nos. 64-9964, 3-221522, 2-304456, 4-11627, 4-175337, 4-18371, 4-31404, and 4-133065. However, any materials have not yet been put to practical use.
According to the report of “Physical Review B46 6705 (1992)” by M. A. Abkowitz et al., it is confirmed that the drift mobility of a high-molecular weight charge transport material is lower than that of a low-molecular weight material by one figure. This report is based on the comparison between the photoconductor comprising a low-molecular weight tetraarylbenzidine derivative dispersed in the photoconductive layer and the one comprising a high-molecular polycarbonate having a tetraarylbenzidine structure in its molecule. The reason for this has not been clarified, but it is considered that the photoconductor employing the high-molecular weight charge transport material produces poor results in terms of the photosensitivity and the residual potential although the mechanical strength of the photoconductor is improved.
To solve the above-mentioned problem, various copolymers having a triarylamine structure were put forward as the high-molecular weight photoconductive materials. Most of these copolymers are in the form of a random copolymer or an alternating copolymer. Although each copolymer includes a charge transporting monomer and a monomer capable of improving the wear resistance, such charge transporting properties and wear resistance improving properties are leveled when those monomers are combined in the form of a random or alternating copolymer. The conventional photoconductors employing the above-mentioned random or alternating copolymers cannot meet the overall requirements.